benecaster_resolve_wall_display_name()

Canonical function for resolving the name shown on community surfaces — the Supporter Wall, [benecaster_member_thanks], and any add-on that needs to display a subscriber’s name consistently. Centralises the three-step resolution chain so calling code does not need to read user meta directly:

1. Wall name (_benecaster_wall_display_name) — the name the subscriber has explicitly
   set for community surfaces.

2. First + last name — first_name and last_name from WordPress user meta,
   space-joined, when no wall name is set.

3. WordPress display name (wp_users.display_name) — the final fallback.

Pass a prefetched row object as $prefetched when iterating a result set that already contains the required user fields to skip the extra get_userdata() call per row.